Easy multiply the first number and do keep change flip
For this case, the first thing we are going to do is assume that all the tests are worth the same.
Then, we define a variable:
x: score of Mona's last test
We write now the inequality that models the problem:

From here, we clear the value of x:
Answer:
the lowest grade that Mona can get for her last test so that her test average is 90 or more is:
x = 87
-15 both sides and then it’s will be
5x = 13 then u divide both sides over 5 and the answer will be ( X=2.6 )